This video explains that heat at negative temperatures flows from the negative object to the normal object. If the temperature of the normal object is absolute hot, what happens with the heat? The heat can't be transferred to the absolute hot object, and it apparently does not flow in the other direction, so what happens to it?

1 Answer
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"Absolute Hot" is a cute phrase, but meaningful only in a limited context, where the concept of negative temperature applies. That is, there's a finite number of energy levels in a finite energy range, and whatever particles/quanta/excitations we're studying stay in that context. For example we may be interested in spins of nuclei in a crystal, and how they are affected by magnetic fields.

If a system is at "absolute hot" and you add a bit more energy, the system will be excited in some way making use of energy levels outside (not necessarily above, but probably) the finite range, breaking some contraints (or assumptions) about the system under study. For the nuclear spins example, maybe some atoms become dislodged from the lattics, or the electrons take up the energy in all the marvelous ways described in condensed matter physics. Electrons have no upper limit - they can always escape from the crystal with arbitrarily great escape velocities.

In other words: something will break, changing the system from what it was during discussion of negative temperatures, to something more general. Energy will find a way in, if you force it.

At best, added quanta of energy, such as photons or phonons, will bounce off (a pure white object) or pass through (transparency).